<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <style>
  div {
    width: 50px;
    height: 50px;
    background: blue;
    animation: move 20s 20s linear;
    animation-fill-mode: forwards;
  }

  @keyframes move {
    to {
      margin-left: 200px;
    }
  }
  </style>
</head>
<body>
  <div></div>
  <div class="rate"></div>
  <script>
    "use strict";

    var el = document.querySelector(".rate");
    var ani = el.getAnimations()[0];
    ani.playbackRate = 2;
  </script>
</body>
</html>
